Valve mechanism for an internal combustion engine

ABSTRACT

A valve drive mechanism for actuating a valve of an internal combustion engine includes a camshaft that is rotated by a crankshaft of the internal combustion engine. The crankshaft has a cam with positive and negative acceleration portions. A swing member rocked on a support shaft by rotation of the cam. The swing member has a cam surface configured to drive the valve. The cam surface has a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion. The ramp portion is configured such that when the positive or negative acceleration portions of the cam actuate the swing member, a lift speed of the valve is substantially constant.

PRIORITY INFORMATION

This application is a continuation of PCT Application No. 2004JP12191, filed on Aug. 25, 2004, which claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2003-208562, filed on Aug. 25, 2003, the entire contents of these applications are expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a valve drive mechanism and, more particularly, to a valve drive mechanism for an internal combustion engine.

2. Description of the Related Art

An example of a valve drive mechanism is described in Japanese Patent Document JP-B-3380582. This document discloses a variable valve drive mechanism that includes a drive cam having a tapered cam surface. A swing member having a cam surface comes into sliding contact with a valve. A cam follower comes into sliding contact with the cam surface of the drive cam. The swing member is rocked by rotating the drive cam to thereby open/close the valve. Valve timing is made variable by changing the relative axial positions of the drive cam and swing member.

In such a valve drive mechanism, the configurations of the cam surfaces of the drive cam and of the swing member can be set in such a manner that a resultant acceleration of valve lift defined as the sum of the acceleration component due to the drive cam and the acceleration component due to the swing member does not change before and after the variable valve timing operation. In addition, a positive acceleration component in the cam surface of the swing member and a positive acceleration component in the cam surface of the drive cam can be configured such that they do not overlap each other during the valve lift process but instead the positive acceleration component of the drive cam precedes the positive acceleration component of the swing member.

SUMMARY OF THE INVENTION

However, an aspect of the present invention is the recognition that in the case of an arrangement which adopts the structure as described above and which uses a shim, a screw, or the like to perform the positional adjustment of a manual lash adjustor, a valve clearance is set in advance, so a ramp portion (buffer section) becomes necessary at the time of valve lift. From the viewpoints of valve system noise and controllability of intake air amount, it is desired that the configuration of the ramp portion be set to exhibit a predetermined characteristic from large opening to small opening. However, since which range of the rotating cam is used differs between that at the time of large opening and that at the time of small opening, the range of the rotating cam to be used during use of the ramp portion also exhibits different characteristics between large opening and small opening settings. Accordingly, in cases where the ramp portion is used, it is difficult to impart the same valve opening/closing characteristic to the ramp portion of valve lift between the large opening and small opening settings.

In view of this, it is an object of the present invention to provide a valve mechanism for an internal combustion engine which makes it possible to attain a desired characteristic even in the case of a setting in which the acceleration section of a rotating cam is used by the ramp potion of a swing member.

Accordingly, one aspect of the present invention is a valve drive mechanism for actuating a valve of an internal combustion engine. The mechanism includes a camshaft that is rotated by a crankshaft of the internal combustion engine. The crankshaft has a cam with positive and negative acceleration portions. A swing member rocked on a support shaft by rotation of the cam. The swing member has a cam surface configured to drive the valve. The cam surface has a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion. The ramp portion is configured such that when the positive or negative acceleration portions of the cam actuate the swing member, a lift speed of the valve is substantially constant.

Another aspect of the present invention comprises a valve drive mechanism for actuating a valve of an internal combustion engine in which the valve drive mechanism comprises a camshaft. The camshaft is rotated by a crankshaft of the internal combustion engine. The camshaft comprises a cam that has positive and negative acceleration portions. A swing member is reciprocally pivoted by rotation of the cam. The swing member comprises a cam surface having a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion. A variable drive mechanism is configured to vary a lift amount of the valve. The ramp portion is configured such that when the positive or negative acceleration portions of the cam actuate the swing member a lift speed of the valve is substantially constant.

Another aspect of the present invention is a valve drive mechanism for actuating a valve of an internal combustion engine. The valve drive mechanism comprises a cam rotated by a crankshaft of the internal combustion engine. The cam comprises positive or negative acceleration portions. A swing member is reciprocally moved by rotation of the cam. The swing member comprises a cam surface for driving the valve. The cam surface comprises a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion. A variable drive mechanism is configured to adjust a lift amount of the valve between a maximum valve opening setting and a minimum valve opening setting. The valve drive mechanism is configured such that when the positive or negative acceleration portions of the cam actuate the swing member, a lever ratio of the swing member or a rocker arm actuated by the swing member increases as the lift amount is adjusted into the minimum valve opening setting.

BRIEF DESCRIPTION OF THE DRAWINGS

A general architecture that implements various features of specific embodiments of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.

FIG. 1 is a cross-sectional side view of a valve drive mechanism for an internal combustion engine according to a first embodiment of the present invention. The valve drive mechanism is shown in a position in which maximum lift is required and an intake valve of the valve drive mechanism is in a closed state.

FIG. 2 is a cross-sectional side view of the valve mechanism of FIG. 1 with valve drive mechanism in a position in which minimum lift is required and an intake valve of the valve drive mechanism is in a closed state.

FIGS. 3(a) and 3(b) are side and bottom views of a swing member of the valve drive mechanism of FIG. 1.

FIG. 4 is a graph illustrating a relationship between rotating and swing members and valve lift in the valve drive mechanism of FIG. 1.

FIG. 5 is a graph showing a related art example of the relationship between rotating and swing members and valve lift.

FIG. 6 is a cross-sectional side view of a second embodiment of a valve drive mechanism when the maximum lift amount is required and an intake valve is closed.

FIG. 7 is a cross-sectional view of the valve mechanism of FIG. 6 of the present when the maximum lift amount is required and the intake valve is open.

FIG. 8 is a cross-sectional view of the valve mechanism of FIG. 6 of the present when the minimum lift amount is required and the intake valve is closed.

FIG. 9 is a cross-sectional view of the valve mechanism of FIG. 6 of the present when the minimum lift amount is required and the intake valve is open.

FIGS. 10(a) and 10(b) are side and bottom views showing a swing member according to the embodiment of FIG. 6.

FIG. 11 is a graph illustrating the relationship between rotating and swing members and valve lift according to the embodiment of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference to the drawings. FIGS. 1 through 5 illustrate a first embodiment of the present invention. FIGS. 6-11 illustrate a second embodiment of the present invention.

In FIG. 1, reference numeral I denotes a valve mechanism for an intake valve 11 of an internal combustion engine. The valve mechanism 1 can have a camshaft 2 rotated by a crankshaft (not shown) of an internal combustion engine. A rotating cam 3 can be provided on the camshaft 2. A swing member support shaft 4 can be provided in parallel to the camshaft 2. A swing member 5 can be supported on the swing member support shaft 4 and can be adapted to be rocked or pivoted by the rotating cam 3. A rocker arm 6 can be rocked in synchronization with the swing member 5 to open/close the intake valve 11.

In the embodiments described below, reference will be made to the intake valve 11. However, it should be appreciated that certain features and aspects of these embodiments may also be applied to an exhaust valve. It should also be appreciated that various features, aspects and advantages of the present invention may be used with engines having more than one intake valve and/or exhaust valve, and any of a variety of configurations including a variety of numbers of cylinders and cylinder arrangements (V, W, opposing, etc.). In one embodiment, the construction of the valve drive mechanism 1 can be the same or substantially similar between the intake valve 11 and exhaust valve of the engine. Accordingly, the description of the valve drive mechanism herein will focus on the intake valve side and the exhaust valve side will be omitted.

As shown in FIG. 1, the camshaft 2 can be arranged with its longitudinal direction extending toward the front and back (i.e. in the direction perpendicular to the plane) of FIG. 1. The camshaft 2 can be rotated about a center axis O1 at a half rotational speed of that of the crankshaft of the internal combustion engine.

The rotating cam 3 can be fixed onto the outer peripheral surface of the camshaft 2 and, as shown in FIG. 1, the outer peripheral portion thereof can be configured with a base surface 3 a that can be arc-shaped as seen in side view, and a nose surface 3 b projecting from the base surface 3 a.

As shown in FIG. 4, the nose surface 3 b of the rotating cam 3 can be configured with a positive acceleration section and a negative acceleration section.

Further, a center axis O2 of the swing member support shaft 4 can be arranged in parallel to the center axis O1 of the camshaft 2.

The swing member 5 can be in fitting engagement with the outer peripheral surface of the swing member support shaft 4, and can be supported so as to be rockable or pivotable about the center axis O2 of the swing member support shaft 4. A cam surface 5 a for rocking the rocker arm 6 can be formed in the lower end portion of the swing member 5.

As shown in FIGS. 1 through 5, in the cam surface 5 a, there are formed an arc-shaped base circle portion 5 c around the center axis O2, a lift portion 5 d for pressing and rocking the rocker arm 6, and a ramp portion 5 e extending between the lift portion 5 d and the base circle portion 5 c.

The configuration of the ramp portion 5 e can be set to a curved configuration as shown in FIG. 3(a) so that the valve lift speed becomes substantially constant in a setting in which the negative acceleration section of the rotating cam 3 is used by the ramp portion 5 e as shown in FIG. 4.

In this embodiment, the ramp portion 5 e can be formed in a curved configuration so as to generate positive acceleration so that the valve lift speed becomes constant in the setting in which the negative acceleration section of the rotating cam 3 is used by the ramp portion 5 e under a state where the lift amount can be variably controlled to be within a minimum range. The details in this regard are described later.

Further, as shown in FIG. 3(b), a width L1 of the base circle portion 5 c can be formed smaller than a width L2 of the lift portion 5 d.

Further, a roller shaft 7 having a center axis O3 in parallel to the center axis O2 of the swing member support shaft 4 can be arranged at the longitudinally middle portion of the swing member 5. Provided to the roller shaft 7 can be a roller 8 that contacts and operates in synchronization with the base surface 3 a or the nose surface 3 b of the rotating cam 3, for transmitting the drive force from the rotating cam 3 to the swing member 5.

Further, a spring 15 for urging the swing member 5 toward the rotating cam 3 side can be in fitting engagement with the swing member support shaft 4. Thus, the swing member 5 can be urged toward the rotating cam 3 side by the urging force of the spring 15, so that the outer peripheral surface of the roller 8 can be in constant contact with the base surface 3 a or nose surface 3 b of the rotating cam 3.

Furthermore, the valve mechanism 1 can be provided with a variable abutment portion mechanism as described below that makes variable the relative distance between a roller 14 and a center axis O5 of a rocker arm shaft 12 which will be described later.

That is, the rocker arm 6 has a rocker arm main body 6 d provided so as to be turnable by the rocker arm shaft 12, and the roller 14 can be supported on the rocker arm main body 6 d through a roller arm 6 c.

Specifically, as shown in FIG. 1, an eccentric shaft 29 can be fixedly provided to the rocker arm shaft 12 in such a manner that a center axis O7 of the eccentric shaft 29 can be located in parallel and eccentrically to the center axis O5 of the rocker arm shaft 12. The roller arm 6 c can be rotatably locked onto the eccentric shaft 29 by means of a leaf spring 28, for example.

The roller arm 6 c has an engaging portion 6 e formed at its one end. The engaging portion 6 e engages with the outer peripheral surface of the eccentric shaft 29, and can be so shaped as to be capable of sliding on the outer peripheral surface of the eccentric shaft 29. A fitting engagement portion 6 f can be projectingly disposed in the position adjacent to the engaging portion be to come into fitting engagement with the leaf spring 28 so as to prevent dislodging thereof.

The leaf spring 28 can be formed into a predetermined configuration by bending a planar spring at several locations. A locking portion 28 a formed in the leaf spring 28 can be brought into fitting engagement with the fitting engagement portion 6 f and the eccentric shaft 29, whereby the roller arm 6 c and the eccentric shaft 29 are integrally locked in place. Further, a distal end portion 28 b of the leaf spring 28 can be brought into elastic contact with a contact surface 6 i of the rocker arm main body 6 d. Accordingly, the roller arm 6 c can be urged clockwise in FIG. 1 by the leaf spring 28, causing the roller 14 to abut the cam surface 5 a of the swing member 5. Further, a predetermined clearance A can be provided between a pressing portion 6 h of the roller arm 6 c and a guide portion 6 j of the rocker arm main body 6 d.

The roller 14 can be rotatably supported on a roller shaft 13 that can be in fitting engagement with a through-hole 6 g at the distal end portion of the roller arm 6 c.

The pressing portion 6 h can be formed on the lower side of the distal end portion of the roller arm 6 c. The guide portion 6 j of the rocker arm main body 6 d can be pressed by the pressing portion 6 h, causing the rocker arm main body 6 d to turn downwardly.

Further, the roller arm 6 c can be freely movable to a predetermined position. By changing the contact position between the roller 14 provided to the roller arm 6 c and the cam surface 5 a of the swing member 5, the life amount of each valve 11 or the like can be adjusted.

Further, formed on the lower side of the distal end portion of the rocker arm main body 6 d can be a valve pressing portion 6 a that presses on the upper surface of a shim 23 fitted on the intake valve 11.

As described above, the roller arm 6 c can be integrally locked onto the eccentric shaft 29 by means of the leaf spring 28 so that the roller arm 6 c can slide on the outer peripheral surface of the eccentric shaft 29. Thus, when the swing member 5 can be rocked, the roller arm 6 c can be rocked via the roller 14 and the roller shaft 13 toward the intake valve 11 side against the urging force of the leaf spring 28. Further, as the roller arm 6 c can be rocked toward the intake valve 11 side, the pressing portion 6 h of the roller arm 6 c presses on the guide portion 6 j of the rocker arm main body 6 d to cause the rocker arm main body 6 d to rock toward the intake valve 11 side, thereby making it possible to open the intake

Further, an actuator (not shown) for rotating the rocker arm shaft 12 within a predetermined angle range about the center axis O5 can be connected to one end portion of the rocker arm shaft 12. Connected to the actuator can be control means (not shown) for controlling the angle of the actuator according to the operational state of the internal combustion engine.

Thus, when the rocker arm shaft 12 is rotated by a predetermined angle by the actuator, the eccentric shaft 29 provided to the rocker arm shaft 12 can be turned by a predetermined angle about the center axis O5 of the rocker arm shaft 12. Further, when the eccentric shaft 29 is turned by the predetermined angle, the roller arm 6 c operating in synchronization therewith can be moved, for example, from the position shown in FIG. 1 to a predetermined position shown in FIG. 2. Then, once the roller arm 6 c has been moved to the predetermined position, the contact point where the cam surface 5 a of the swing member 5 and the roller 14 provided to the roller arm 6 c come into contact with each other changes. The rocking amount of the rocker arm main body 6 d can be thus changed, which the lift amount or the like of the intake valve 11 that can be vertically moved by the rocker arm 6 can be adjusted.

Here, the lever ratio of the rocker arm 6 pressed on by the swing member 5 can be adapted to increase as the roller arm 6 c can be moved from the state shown in FIG. 1 to the state shown in FIG. 2 and as the lift amount can be variably controlled to be within a minimum range. That is, while the rocker arm main body 6 d turns about the center axis O5, the pressing portion 6 h of the roller arm 6 c approaches the center axis O5 as the lift amount can be variably controlled to be within a minimum range. The lever ratio of the rocker arm 6 can be adapted to increase with this approaching movement.

Further, even in the case where a predetermined clearance is not provided between the valve pressing portion 6 a of the rocker arm main body 6 d and the intake valve 11, the predetermined clearance A provided between the pressing portion 6 h and the guide portion 6 j allows the intake valve 11 to be reliably opened and closed even when, due to a rise in the temperature of the internal combustion engine, the intake valve 11 undergoes thermal expansion to cause elongation of the valve.

With the valve mechanism 1 for an internal combustion engine constructed as described above, in which the lift amount of each valve 11 or the like can be adjusted by making the roller arm 6 c be freely movable to the predetermined position and changing the contact position between the roller 14 of the rocker arm 6 and the cam surface 5 a of the swing member 5, the roller arm 6 c can be urged toward the swing member 5 side by the leaf spring 28. Accordingly, even when the roller arm 6 c can be moved to the predetermined position and the contact position between the roller 14 and the cam surface 5 a changes, the roller 14 of the rocker arm 6 and the cam surface 5 a of the swing member 5 meet each other, thereby making it possible to prevent adhesive wear.

Further, although the width L1 of the base circle portion 5 c can be small, since no large load acts on this portion, a requisite strength can be secured for the base circle portion 5 c. Because a large load acts on the lift portion 5 d, the width L2 thereof can be made larger to secure a requisite strength.

Further, the rocker arm 6 can be disposed below the swing member 5 while being rockably supported on the rocker arm shaft 12.

The intake valve 11 has a collet 20 and an upper retainer 21 that are provided in its upper portion. A valve spring 22 can be arranged below the upper retainer 21. The intake valve 11 can be urged toward the rocker arm 6 side by the urging force of the valve spring 22. Further, the shim 23 can be fitted on the upper end portion of the intake valve 11.

Accordingly, the intake valve 11 can be vertically moved by rocking the rocker arm 6 in synchronization with the rocking motion of the swing member 5. Thus, the maximum lift amount of the intake valve 11 can be made variable by making the relative distance between the center axis O5 of the rocker arm shaft 12 and the roller 14 variable.

A shown in FIG. 4, in the illustrated embodiment, by forming the ramp portion 5 e of the swing member 5 in a predetermined curved configuration and imparting positive acceleration to the ramp portion 5 e of the swing member 5, the speed of the ramp portion 5 e of the valve lift becomes substantially constant in the state where the lift amount is minimum. Accordingly, even when changes in valve clearance occur due to variations in the accuracy of finishing of the components or due to changes in the dimensions of the components resulting from thermal expansion, variations in valve opening/closing timing can be stabilized. Since combustion can be stabilized, the output performance or exhaust gas performance can be made stable, and further the impact of the valve when it returns to the seat or the valve system vibration can be stabilized to stabilize noise.

In this regard, FIG. 4 is a graph illustrating the relationship among three components: the rotating and swing members and the valve lift, according to the first embodiment, and FIG. 5 is a graph illustrating the relationship among three components: the rotating and swing members and the valve lift, according to the prior art.

In those figures, corresponding points of two of the three components are shown by chain double-dashed lines. Turning now to the rotating cam, the horizontal axis represents the rotation angle of the rotating cam 3, and the vertical axis represents the lift amount of the rotating cam 3. The figures show a lift curve (A) of the rotating cam 3.

Further, in the graph shown in FIG. 4, the foot portion (the foot portion of the nose surface 3 b) of the lift curve (A) can be curved, and as indicated by an acceleration curve (B) drawn in broken line, this portion serves as the positive acceleration section.

Further, in the lift curve (A), the portion above the foot portion (the portion other than the foot of the nose surface 3 b) can be curved, and this portion serves as the negative acceleration section as indicated by a characteristic curve (H) drawn in broken line.

Turning now to the swing member, the horizontal axis on the left represents the lift amount of the swing member. When, as described above, the valve lift can be set at minimum opening, the swing member 5 exhibits a lift characteristic as indicated by a curve (D). In the figures, symbol (a) represents a characteristic at the ramp portion 5 e, and symbol (b) represents a characteristic at the lift portion 5 b.

Turning now to the valve lift, the vertical axis on the lower side represents the lift amount. The lift curve (D) of the swing member 5 and the lift curve (A) of the rotating cam 3 are synthesized to obtain a lift curve (F) of the valve lift.

In the illustrated embodiment case, the characteristic (a) of the ramp portion 5 e generating positive acceleration and the characteristic (c) of the rotating cam 3 generating negative acceleration are synthesized, so a ramp portion characteristic (d) of the lift curve (F) at minimum valve lift exhibits a straight line (see FIG. 4), that is, constant valve lift speed. Thus, even when a variation occurs in valve clearance in the state where the ramp portion 5 e can be in contact with the roller 14, the valve opening/closing timing can be stable, thereby achieving enhanced controllability of the intake air amount.

On the other hand, when, as described above, the valve lift can be set at its maximum, the rotating cam 5 exhibits a characteristic indicated by a curve (E). In the figures, symbol (a) represents a characteristic at the ramp portion 5 e, and symbol (b) represents a characteristic at the lift portion 5 b.

The lift curve (E) of the swing member 5 and the lift curve (A) of the rotating cam 3 are synthesized to obtain a valve lift characteristic curve (G).

By synthesizing the characteristic (a) of the ramp portion 5 e generating positive acceleration and the characteristic (e) of the rotating cam 3 generating positive acceleration, a ramp portion characteristic (f) of the lift curve (G) at maximum valve lift generates positive acceleration.

It should be noted that in the prior art design shown in FIG. 5, the foot portion (the foot portion of the nose surface 3 b) of the lift curve (A) can be curved, and as indicated by the acceleration curve (B) drawn in broken line, this portion serves as the positive acceleration section.

Further, the middle portion (the middle portion of the nose surface 3 b) of the lift curve (A) can be linear, and this portion serves as a constant speed section.

Further, in the lift curve (A), the upper side portion (the portion near the top of the nose surface 3 b) can be curved, which serves as the negative acceleration section as indicated by a characteristic curve (H) drawn in broken like.

Further, when, as described above, the valve lift can be set at its minimum, the swing member 5 exhibits a characteristic as indicated by the lift curve (D). In the figures, symbol (a) represents a characteristic at the ramp portion 5 e, and symbol (b) represents a characteristic at the lift portion 5 d.

The lift curve (D) of the swing member 5 and the lift curve (A) of the rotating cam 3 are synthesized to obtain the valve lift curve (F).

The characteristic (a) of the ramp portion 5 e exhibiting constant speed and the characteristic (c) of the rotating cam 3 having negative acceleration are synthesized, so the initial characteristic (d) of the lift curve (F) at small valve lift opening exhibits negative acceleration. Thus, when a variation occurs in the angle of the rotating cam 3 in the state where the ramp portion 5 e can be in contact with the roller 14, the valve opening/closing timing varies, leading to a deterioration in the controllability of the intake air amount.

Further, in this embodiment, as the lift amount is variably controlled to be within a minimum range, the roller arm 6 c and the roller 14 are moved from the state shown in FIG. 1 to that shown in FIG. 2, whereby the lever ratio of the rocker arm 6 pressed by the swing member 5 increases. Therefore, a decrease in speed at the valve lift characteristic d corresponding to the ramp portion 5 e can be compensated for, whereby the valve lift speed can be readily made linear to thereby suppress variations in valve opening/closing timing.

Further, the rotating cam 3 can be formed in such a configuration allowing the nose surface 3 b to generate acceleration in all the sections. Accordingly, by setting the negative acceleration section of the rotating cam 3 long, and setting the maximum acceleration low, the top portion of the nose surface 3 b of the rotating cam 3 can be made gentle (made to have a large radius of curvature), whereby the requisite force of the spring 15 for bringing the swing member 5 into abutment with the rotating cam 3 can be reduced, and also the vibration of the swing member 5 can be suppressed. Further, since the nose surface 3 b of the rotating cam 3 has the positive and negative acceleration sections formed therein with no constant-speed section, when creating a cam profile, forming profiles for the two kinds of acceleration sections suffices, whereby the cam profile can be readily shaped.

FIGS. 6 through 11 illustrate a second embodiment of the present invention. As will be explained below, in this embodiment, the variable abutment portion mechanism for making the valve lift amount variable can be provided on the swing member 5 side, and desired valve characteristics can be obtained when the opening at maximum lift amount is large.

As shown in FIGS. 6 through 11, in a cam surface 5 a of a rotating cam 5 according to this embodiment, there are formed a base circle portion 5 c having the shape of a circular arc drawn around a center axis O2, a lift portion 5 d for pressing and rocking a rocker arm 6, and a ramp portion 5 e connecting between the lift portion 5 d and the base circle portion 5 c.

The ramp portion 5 e can have a curved configuration. The configuration of the ramp portion 5 e can be set to a curved configuration so that the valve lift speed becomes constant in a setting in which the positive acceleration section of the rotating cam 3 can be used by the ramp portion 5 e. Here, the ramp portion 5 e can be formed in a curved configuration so as to generate negative acceleration so that the valve lift speed becomes constant in the setting in which the positive acceleration section of the rotating cam 3 can be used by the ramp portion 5 e under a state where the lift amount can be variably controlled to be within a maximum range.

Further, as shown in FIG. 10, a width L1 of the base circle portion 5 c can be formed smaller than a width L2 of the lift portion 5 d.

Further, a guide portion 5 b as an elongate through-hole can be formed at the longitudinally middle portion of the swing member 5. A roller shaft 7, which has a center axis O3 in parallel to the center axis O2 of a swing member support shaft 4, can be movably inserted through the guide portion 5 b. Provided to the roller shaft 7 can be a roller 8 that contacts and operates in synchronization with a base surface 3 a or a nose surface 3 b of the rotating cam 3, for transmitting the drive force from the rotating cam 3 to the swing member 5.

Further, the guide portion 5 b can be formed in the shape of an elongate hole to guide the roller shaft 7 along its longitudinal direction over a predetermined distance, and the guiding direction at this time can be inclined with respect to the radial direction of the camshaft 2.

As shown in FIG. 6, the roller 8 can be formed in a circular shape, and can be arranged on the outer peripheral surface of the roller shaft 7 so that the center axis of the roller 8 becomes the same as the center axis O3 of the roller shaft 7. The outer peripheral surface of the roller 8 can be capable of rolling on the base surface 3 a and nose surface 3 b of the swing member 3.

Here, the roller 8 used can be capable of rolling on the surface of the rotating cam 3. However, the present invention is not limited to this; the roller 8 used may be one capable of sliding on the surface of the rotating cam 3 as long as the drive force from the rotating cam 3 can be transmitted to the swing member 5.

Further, a spring 15 for urging the swing member 5 toward the rotating cam 3 side can be in fitting engagement with the swing member support shaft 4. Thus, the swing member 5 can be urged toward the rotating cam 3 side by the urging force of the spring 15, so that the outer peripheral surface of the roller 8 can be in constant contact with the base surface 3 a or nose surface 3 b of the rotating cam 3.

Furthermore, the valve mechanism 1 can be provided with a variable abutment portion mechanism for making variable the relative distance between the roller 8 and the center axis O2 of the swing member support shaft 4.

The variable abutment portion mechanism has a drive shaft 9 fixedly provided onto the swing member support shaft 4, and an arm 10 whose one end portion 10 a can be connected to the roller shaft 7 and whose other end portion 10 b can be connected to the drive shaft 9.

The drive shaft 9 can be provided to the swing member support shaft 4 in such a manner that a center axis O4 thereof can be located in parallel and eccentrically to the center axis O2 of the swing member support shaft 4.

Further, an actuator (not shown) for rotating the swing member support shaft 4 within a predetermined angle range about the center axis O2 can be connected to one end portion of the swing member support shaft 4. Connected to the actuator can be control means (not shown) for controlling the angle of the actuator according to the operational state of the internal combustion engine.

Thus, when the swing member support shaft 4 turns by a predetermined angle, the drive shaft 9 turns by a predetermined angle about the center axis O2 of the swing member support shaft 4, whereby the position of the center axis O4 changes relative to the center axis O2 of the swing member support shaft 4.

The arm 10 can be capable of keeping the distance between the center axis O3 of the roller shaft 7 and the center axis O4 of the drive shaft 9 constant. A through-hole 10 c, with which the roller shaft 7 can be fitted, can be formed at the one end portion 10 a of the arm 10, and an insertion portion 10 d, into which the drive shaft 9 can be inserted and which can be partially open, can be formed at the other end portion 10 b thereof. Accordingly, the roller shaft 7 can be rotatably fitted with the through-hole 10 c at the one end portion 10 a, and the drive shaft 9 can be rotatably fitted with the insertion portion 10 d at the other end portion 10 b and mounted in place with a pin 16 so as to prevent dislodging thereof.

Thus, when the swing member support shaft 4 is rotated by a predetermined angle by the actuator, the drive shaft 9 provided to the swing member support shaft 4 can be turned by a predetermined angle about the center axis O2 of the swing member support shaft 4, and the roller shaft 7 can be operated in synchronization with this turning movement through the arm 10. The roller shaft 7 can be thus moved within the guide portion 5 b while keeping the distance between the center axis O3 of the roller shaft 7 and the center axis O4 of the drive shaft 9 constant with the arm 10, whereby the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 8 can be made variable.

Here, the lever ratio of the rocker arm 6 pressed on by the swing member 5 can be adapted to increase as the roller arm 6 c can be moved from the state shown in FIG. 6 to the state shown in FIG. 8 and as the lift amount can be variably controlled to be within a minimum range. That is, while the swing member 5 turns about the center axis O2, the roller shaft 7 pressing on the guide portion 5 b approaches the center axis O2 as the lift amount can be variably controlled to be within a minimum range. The lever ratio of the swing member 5 can be adapted to increase with this approaching movement.

Further, the rocker arm 6 can be disposed below the swing member 5 while being rockably supported on the rocker arm shaft 12.

Further, a valve pressing portion 6 a can be formed at the distal end portion of the rocker arm 6 for pressing on the upper surface of a shim 23 fitted on an intake valve 11 which will be described later.

A roller 14 can be rotatably provided to the roller shaft 13, and the outer peripheral surface of the roller 14 can be capable of rolling on the cam surface 5 a of the swing member 5.

Further, a spring 17 for urging the rocker arm 6 toward the swing member 5 side can be in fitting engagement with the rocker arm shaft 12. Thus, the rocker arm 6 can be urged toward the swing member 5 side by means of the spring 17, so that the outer peripheral surface of the roller 14 can be in constant contact with the cam surface 5 a of the swing member 5.

Further, the intake valve 11 pressed by the valve pressing portion 6 a can be arranged below the valve pressing portion 6 a of the rocker arm 6 so as to be vertically movable.

The intake valve 11 has a collet 20 and an upper retainer 21 that are provided in its upper portion. A valve spring 22 can be arranged below the upper retainer 21. The intake valve 11 can be urged toward the rocker arm 6 side by the urging force of the valve spring 22. Further, the shim 23 can be fitted on the upper end portion of the intake valve 11.

Accordingly, the intake valve 11 can be vertically moved by rocking the rocker arm 6 in synchronization with the rocking motion of the swing member 5. Thus, by making the relative distance between the center axis O2 of the swing member 4 and the roller 8 variable to adjust the rocking start position of the swing member 5, the maximum lift timing of the intake valve 11 can be adjusted and made variable through the rocker arm 6.

Next, the operation of the valve mechanism 1 constructed as described above will be described.

First, detailed description will be made on the operation of the valve mechanism 1 for an internal combustion engine when the maximum lift amount is required.

Here, FIG. 6 is a cross-sectional side view of the main portion of valve mechanism 1 of the internal combustion engine when the maximum lift amount is required; illustrating the state in which the intake valve 11 is closed. FIG. 7 is a cross-sectional side view of the main portion of the valve mechanism 1 of the internal combustion engine when the maximum lift amount is required, illustrating the state in which the intake valve is open.

First, as shown in FIG. 6, the roller shaft 7 can be moved to the rotating cam 3-side end portion of the guide portion 5 b, thereby changing the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 8. That is, the swing member support shaft 4 can be turned by a predetermined angle by the actuator, causing the drive shaft 9 to move in the circumferential direction of the swing member support shaft 4. Thus, the roller shaft 7 can be operated in synchronization with this movement via the arm 10 to be moved to the rotating cam 3-side end portion of the guide portion 5 b, whereby the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 8 changes.

Further, as shown in FIG. 6, while the roller 8 provided to the swing member 5 can be in contact with the base surface 3 a of the rotating cam 3, the swing member 5 is not rocked to the intake valve 11 side, the rocker arm 6 can be urged to the swing member 5 side by the urging force of the spring 17, and also the intake valve 11 can be urged to the rocker arm 6 side by the urging force of the valve spring 22. Thus, the lift of the intake valve 11 does not occur and the intake valve 11 can be brought into a closed state.

In this state, the roller 14 can be located at the position corresponding to the base circle portion 5 c of the cam surface 5 a of the swing member 5. Since no large abutment force acts between the roller 14 and the base circle portion 5 c in the valve closure state, a sufficient durability can be secured even through the width L1 of the base circle portion 5 c can be small.

Then, when the rotating cam 3 is rotated via the camshaft 2 due to the rotation of the crankshaft of the internal combustion engine, as shown in FIG. 7, the roller 8 can be pressed on by the nose surface 3 b. As the roller 8 is further pressed, the swing member 5 can be pressed via the roller shaft 7, causing the swing member 5 to rock counterclockwise in FIG. 6 against the urging force of the spring 15.

Through the rocking movement of the swing member 5, the portion of the cam surface 5 a of the swing member 5 which presses the roller 14 changes from the base circle portion 5 c to the lift portion 5 d via the ramp portion 5 e, and the rocker arm 6 can be turned via the roller shaft 13 to the intake valve 11 side. In this way, a relative distance M between the center axis O2 of the swing member support shaft 4 and the roller 14 in contact with the cam surface 5 a of the swing member 5 as shown in FIG. 6 is largely changed to a relative distance N between the center axis O2 of the swing member support shaft 4 and the roller 14 in contact with the cam surface 5 a of the swing member 5 as shown in FIG. 7. The rocker arm 6 thus undergoes large rocking movement to the intake valve 11 side.

Then, the valve pressing portion 6 a formed at the distal end portion of the rocker arm 6 that has thus undergone large rocking movement to the intake valve 11 side presses on the upper surface of the shim 23 to push down the intake valve 11 by a large distance. As described above, by moving the roller shaft 7 to the end portion of the guide portion 5 b in the rotating cam 3 side to make the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 8 variable, the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 14 in contact with the cam surface 5 a of the swing member 5 can be largely changed, whereby the intake valve 11 can be pushed down by a large distance to bring the intake valve 11 into an open state at the maximum lift amount.

In the case where the intake valve 11 is opened in this way, the width L2 of the lift portion 5 d can be made large because a large reaction force acts on the cam surface 5 a of the swing member 5, thereby making it possible to secure strength.

Next, detailed description will be made on the operation of the valve mechanism 1 of the internal combustion engine when the minimum lift amount is required.

Here, FIG. 8 is a cross-sectional side view of the main portion of the valve mechanism when the minimum lift amount is required, illustrating the state in which the intake valve is closed. FIG. 9 is a cross-sectional view of the main portion of the valve mechanism when the minimum lift amount is required, illustrating the state in which the intake valve is open.

First, as shown in FIG. 8, in the state as shown in FIG. 6 where the roller shaft 7 can be retained at the rotating cam 3-side end portion, the roller shaft 7 can be moved to the swing member support shaft 4-side end portion of the guide portion 5 b, thereby changing the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 8.

That is, the swing member support shaft 4 can be turned within a predetermined angle range by the actuator, and the drive shaft 9 can be moved in the circumferential direction of the swing member support shaft 4. Accordingly, the roller shaft 7 can be operated in synchronization with this movement via the arm 10 so that the roller shaft 7 can be moved to the swing member support shaft 4-side end portion of the guide portion 5 b from the state where it is retained at the rotating cam 3-side end portion, whereby the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 8 decreases. Then, the swing member 5 turns from the position as shown in FIG. 6 to the position as shown in FIG. 8 due to the urging force of the spring 15.

Further, as shown in FIG. 8, while the roller 8 provided to the swing member 5 can be in contact with the base surface 3 a of the rotating cam 3, the swing member 5 is not rocked to the intake valve 11 side, the rocker arm 6 can be urged to the swing member 5 side by the urging force of the spring 17, and also the intake valve 11 can be urged to the rocker arm 6 side by the urging force of the valve spring 22. Thus, the lift of the intake valve 11 does not occur and the intake valve 11 can be brought into a closed state.

When the rotating cam 3 is rotated via the camshaft 2 due to the rotation of the crankshaft of the internal combustion engine, as shown in FIG. 9, the roller 8 can be pressed on by the nose surface 3 b, and the swing member 5 can be pressed via the roller shaft 7, causing the swing member 5 to rock counterclockwise in FIG. 8 against the urging force of the spring 15.

As the swing member 5 is further rocked, the roller 14 in contact with the swing member support shaft 4-side distal end portion of the cam surface 5 a of the swing member 5 can be pushed down to the intake valve 11 side by using the range of the cam surface 5 a from the swing member support shaft 4-side distal end portion to the center portion thereof, whereby the rocker arm 6 can be rocked to the intake valve 11 side via the roller shaft 13. In this way, a relative distance P between the center axis O2 of the swing member support shaft 4 and the roller 14 in contact with the cam surface 5 a of the swing member 5 as shown in FIG. 8 undergoes a small change to become a relative distance Q between the center axis O2 of the swing member support shaft 4 and the roller 14 in contact with the cam surface 5 a of the swing member 5 as shown in FIG. 9. The rocker arm 6 thus undergoes small rocking movement to the intake valve side.

Then, the valve pressing portion 6 a formed at the distal end portion of the rocker arm 6 that has thus undergone small rocking movement to the intake valve 11 side presses on the upper surface of the shim 23 to push down the intake valve 11 by a small distance. In this way, by moving the roller shaft 7 to the swing member support shaft 4-side end portion of the guide portion 5 b to make the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 8 variable, the relative distance between the center axis O2 of the swing member support shaft 4 and the roller 14 in contact with the cam surface 5 a of the swing member 5 can be subjected to a small change to push down the intake valve 11 by a small distance, whereby, in Embodiment 1, the intake valve 11 can be brought into an open state at the minimum lift amount.

In the valve mechanism 1 of the internal combustion engine constructed as described above, the swing member 5 can be provided with the roller 8 that comes into contact with the rotating cam 3 to transmit the drive force from the rotating cam to the swing member 5. The valve mechanism 1 can be provided with the variable abutment portion mechanism for making the relative distance between the roller 8 and the center axis O2 of the swing member support shaft 4 variable by making the roller 8 movable; the lift amount or the like of each valve can be made variable by thus making the relative distance variable, whereby the structure can be simplified to achieve low-cost construction.

Further, the load from the rotating cam 3 can be input to the roller 8, and the load can be directly transmitted from the roller 8 to the guide portion 5 a of the swing member 5. Then, the load can be transmitted from the swing member 5 to the intake valve 11 via the rocker arm 6. Thus, no large load acts on the arm 10 that supports the roller 8, and since the arm 10 serves the sole function of moving the roller 8 along the guide portion 5 b, not so large strength is required for the arm 10.

Incidentally, according to the present embodiment, the lift portion 5 d of the swing member 5 can be formed in the predetermined curved configuration, and the ramp portion 5 e of the swing member 5 can be imparted with negative acceleration. Thus, at the initial valve lift stages in a large valve lift opening state, the valve speed becomes constant, thereby reducing the impact at the time of large lift opening.

In this connection, FIG. 11 shows a lift curve (A) of the rotating cam 3, in which the horizontal axis represents the rotation angle of the rotating cam 3, and the vertical axis represents the lift of the rotating cam 3. The foot portion (the foot portion of the nose surface 3 b) of the lift curve (A) is curved, and as indicated by an acceleration curve (B) drawn in broken line, this portion serves as the positive acceleration section.

Further, in the lift curve (A), the portion above the foot portion (the portion other than the foot of the nose surface 3 b) is curved, and this portion serves as the negative acceleration section as indicated by a characteristic curve (H) drawn in broken line.

Further, when, as described above, the valve lift can be set at large opening, the swing member 5 exhibits a lift characteristic as indicated by a curve (E). In the figure, symbol (a) represents a characteristic at the ramp portion 5 e, and symbol (b) represents a characteristic at the lift portion 5 b.

The lift curve (E) of the swing member 5 and the lift curve (A) of the rotating cam 3 are synthesized to obtain a valve lift curve (G).

The characteristic (a) of the ramp portion 5 e having negative acceleration and a characteristic (e) of the rotating cam 3 having positive acceleration are synthesized, so an initial characteristic (f) of the lift curve (G) at large valve lift opening exhibits substantially constant speed. Thus, a reduction in impact can be achieved in the state where the ramp portion 5 e can be in contact with the roller 14.

On the other hand, when, as described above, the valve lift can be set at small opening, the rotating cam 5 exhibits a characteristic indicated by a curve (E).

The characteristic (a) of the ramp portion 5 e having negative acceleration and the characteristic (b) of the rotating cam 3 having negative acceleration are synthesized, so the initial characteristic (d) of the lift curve (F) at large valve lift opening has negative acceleration, which means that variations may occur in the valve opening/closing timing. However, when, at the time of large valve lift opening, the engine can be rotating at high speed and the noise impact at the ramp portion 5 e presents a greater problem than such variations in valve timing, it is desirable to adopt Embodiment 2 described above.

Further, in this embodiment, as the lift amount can be variably controlled to be within a minimum range, the arm 10 and the roller 8 are moved as shown in FIGS. 6 through 8, whereby the lever ratio of the swing member 5 increases. Therefore, the speed at the valve lift characteristic (d) corresponding to the ramp portion 5 e can be increased, whereby variations in valve opening/closing timing can be suppressed.

It should be noted that while in above-described embodiments the structure shown in FIG. 1 and the like exhibits the characteristics shown in FIG. 4, and the structure shown in FIG. 6 and the like exhibits the characteristics shown in FIG. 11, this should not be construed restrictively. It is also possible for the structure shown in FIG. 1 and the like to exhibit the characteristics shown in FIG. 11, and for the structure shown in FIG. 6 and the like to exhibit the characteristics shown in FIG. 4.

Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combine with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow. 

1. A valve drive mechanism for actuating a valve of an internal combustion engine, the valve drive mechanism comprising; a camshaft rotated by a crankshaft of the internal combustion engine and comprising a cam, the cam having positive and negative acceleration portions, and a swing member that is configured to be rocked on a support shaft by rotation of the cam, the swing member having a cam surface configured to drive the valve; the cam surface having a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion; wherein the ramp portion is configured such that when the positive or negative acceleration portions of the cam actuate the swing member a lift speed of the valve is substantially constant.
 2. The valve drive mechanism as in claim 1, wherein the valve is an intake valve.
 3. The valve drive mechanism as in claim 1, wherein the valve is an exhaust valve.
 4. The valve drive mechanism as in claim 1, further comprising means for varying the lift of the valve.
 5. A valve drive mechanism for actuating a valve of an internal combustion engine, the valve drive mechanism comprising; a camshaft rotated by a crankshaft of the internal combustion engine and comprising a cam, the cam having positive and negative acceleration portions, and a swing member that is reciprocally pivoted by rotation of the cam, the swing member comprising a cam surface having a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion, and a variable drive mechanism configured to vary a lift amount of the valve; wherein the ramp portion is configured such that when the positive or negative acceleration portions of the cam actuate the swing member a lift speed of the valve is substantially constant.
 6. The valve drive mechanism as in claim 5, wherein the ramp portion is configured to provide positive acceleration such that when the variable time mechanism is set in a minimum valve opening position a lift speed of the valve when the valve is being actuated by the ramp portion and the negative acceleration portion of the cam is substantially constant.
 7. The valve drive mechanism as in claim 5, wherein in a setting in which the ramp portion uses a positive acceleration section of the rotating cam under a state where the lift amount is variably controlled to be within a maximum range, the ramp portion is formed in a curved configuration so as to generate negative acceleration so that the lift speed of the valve in the portion corresponding to the ramp portion becomes substantially constant.
 8. The valve drive mechanism as in claim 5, wherein the valve is an intake valve.
 9. The valve drive mechanism as in claim 5, wherein the valve is an exhaust valve.
 10. The valve drive mechanism as in claim 5, wherein the variable valve mechanism comprises a roller arm that is positioned between the swing member and a rocker arm.
 11. The valve drive mechanism as in claim 5, wherein the variable valve mechanism comprises a roller arm that is positioned between the swing member and the cam.
 12. The valve drive mechanism as in claim 5, wherein a width of the base circle portion of the cam surface is smaller than a width of the lift portion of the cam surface.
 13. The valve drive mechanism as in claim 12, wherein the width of the base circle portion of the cam surface is at least 50% smaller than the width of the lift portion of the cam surface.
 14. A valve drive mechanism for actuating a valve of an internal combustion engine, the valve drive mechanism comprising a cam rotated by a crankshaft of the internal combustion engine, the cam comprising positive or negative acceleration portions; a swing member that is reciprocally moved by rotation of the cam, the swing member comprising cam surface for driving the valve; the cam surface comprising a base circle portion, a lift portion, and a ramp portion extending between the base circle portion and the lift portion; and a variable drive mechanism configured to adjust a lift amount of the valve between a maximum valve opening setting and a minimum valve opening setting; wherein the valve drive mechanism is configured such that when the positive or negative acceleration portions of the cam actuate the swing member, a lever ratio of the swing member or a rocker arm actuated by the swing member increases as the lift amount is adjusted into the minimum valve opening setting.
 15. The valve drive mechanism as in claim 14, wherein the cam comprises a base surface, and a nose surface projecting from the base surface, the nose surface of the cam being configured to provide for acceleration of the valve in all sections of the valve.
 16. The valve drive mechanism as in claim 14, wherein the valve drive mechanism includes a gap for absorbing errors or thermal expansion of respective portions of the valve drive mechanism system, the gap exists between components between the swing member and the valve.
 17. The valve drive mechanism as in claim 16, wherein a spring member brings the cam surface into constant contact another component of the valve drive mechanism.
 18. The valve drive mechanism as in claim 14, wherein the valve is an intake valve.
 19. The valve drive mechanism as in claim 14, wherein the valve is an exhaust valve.
 20. The valve drive mechanism as in claim 20, wherein a width of the base circle portion of the cam surface is smaller than a width of the lift portion of the cam surface. 